The Langkilde Lab in Action

This one looks like he might be. Not bad for a deadbeat dad who fertilizes-and-flees.

This spring, I captured wood frog “sex” on video. Since frog eggs are fertilized as they’re being laid, the male wood frog in this video is simultaneously having (his version of) sex and helping to deliver the babies. Wrap your head around that.

Female wood frogs (in this video—the frog that’s underneath) are essentially balloons full of unfertilized eggs when they come to the breeding ponds. When a male finds a female frog, he amplexes her—essentially, he wraps his arms around her from behind, digs in his thumbs, and holds on for dear life. She’ll carry him around for a while like this until she finds the perfect spot in the pond to lay her eggs. At that point, maybe following some trigger that we don’t yet understand, she begins laying eggs.

You’d think that males would just squeeze the eggs out of the females. They’ve got their arms around the female’s balloon-belly, after all. But they also use their shovel-like feet to slowly pull the eggs out of her. Bit by bit, you can see the female’s belly begin to deflate with each male “pull” in this video clip.

In these breeding ponds, there’s fierce competition among males to get a lady. And male wood frogs aren’t too clear on what’s a female, and what isn’t. At 1:50, check out how a lonely male mistakes our busy father for an available lady. It takes the interloper a few moments to realize his mistake… after which he wanders off like nothing out of the ordinary happened.

If you’re in the mood for bad film noir, here’s an alternate version of this video for you to enjoy:

Today I thought it would be fun to share with you something a little different. I recently visited Berkeley, California, and while there I stumbled across a fantastic example of applied ecology. After a long day of planes, trains, and (unfortunately no) automobiles, I took a refreshing walk to McLaughlin Eastshore State Park—as far west as you can go in Berkeley before falling into the San Francisco Bay. Awesome—finally some nature and a chance to recharge. Like any good ecologist, I poked around for a while, and watched egrets and gulls around the mudflats as the sun set over the bay. Naively thinking to myself, “Gee, how swell that the city kept this natural area so nicely preserved!”

Eastshore State Park, CA. Photo credit: L Swierk

Looking back over the Berkeley Meadow to Berkeley. Photo credit: L Swierk

Except… I was entirely wrong. Maybe I should’ve been clued in by the odd shape of the shoreline on the map, and how darn close it was to an old-timey train. After an hour of pleasant investigating, I wandered up to this sign, entitled “What are you standing on?”:

Landfill. Well. A little additional research turned up some information that this was essentially an old hazardous materials dumping site. Did this change the enjoyment I felt from my wildlife-watching and wandering? Heck no. I grinned and felt nerdishly overjoyed at this feat of reclamation. Had I never been told, I would never have guessed. What an awesome success story—they fooled an ecologist!

Over the past several years, I like to think I’ve been a sort-of successful spy on the secret lives of herps. As a behavioral ecologist with a focus on reproductive behavior, invading animal privacy comes as part of the job. Thankfully for my conscience, my subjects don’t seem to mind… or really even notice. One of the plus sides of working on reproductive behavior is that— at least when sex is in the offing—animal subjects seem to care a lot less that big, lumbering, non-predatory researchers are nearby. In this post, I’d like to share with you the delightfully graphic details of one of my spying expeditions on eastern fence lizard (Sceloporus undulatus) sexual competition.

Males of all species tend to fight. A lot. Not exactly a ground-breaking revelation. (Females fight too, but generalizing over all species… let’s face it: males on average tend to fight more.) What is immediately apparent across the animal kingdom is that fighting with males of your same species can be very, very costly. Think about some examples of “classic” male weaponry – antlers, teeth, tusks, horns – they’ve evolved to wound, maim, injure, and even kill.

Figure 1. Male on male combat occurs in many species including serious battles between male southern elephant seals (Mirounga leonina) which use their teeth to gash competitors (Top) and elk which spar with their antlers (Bottom).Images from Wikimedia

Fence lizard males—despite their modest size, lack of obvious weaponry, and generally sweet nature (a spy’s personal opinion)—also can be absurdly aggressive when it comes to sex. Quick natural history lesson: Male fence lizards defend home ranges that abut or overlap those of other males; females have smaller home ranges that are nestled inside one or more male home ranges. When males fight with each other, it’s often over access to females who, from the males’ perspective, wander too much. Females watch males fighting and may make their own mate choice decisions based on what they see. So, you might imagine that it would behoove males to give each fight their all, not only to win the right to the lady, but also to impress her. However, that’s not what we’ve observed. Instead, we see a wide variation in fighting strategies: some male lizards are downright timid, backing down pretty quickly, while others go right for the throat, so to speak.

Above: A bout of territorial competition between two Sceloporus (either graciosus or occidentalis) involving chases and whole-body shudders.

As part of our research, we staged encounters between males to figure out why so much variation exists in how and when males escalate fights. We placed males in a laboratory arena, separated from each other (and a tempting, lovely, lady lizard) by clear glass to prevent any real bloodshed between competing males. Instead of observing who the winners and losers of real, pitched lizard battles were, we used an excellent indicator of contest escalation—display behavior. Display behaviors are body postures and movements that convey messages to competitors, for instance, lizard “pushups” and whole-body shuddering that are signals of territory assertion. Using video recordings, we carefully documented every display behavior each male sent to his competitor—essentially transcribing a non-verbal dialogue between two increasingly angry males. We were able to “decode” this dialogue, assisted by information collected and previously published by other researchers around the world. And what we found after decoding these secret messages was pretty surprising.

Figure 2. A diagram of the arena used in trials of display behavior for Sceloporus. Males were placed in the two side areas and could view a centrally placed female and the other male through clear dividers.

Because fighting can be so costly (not only is fighting exhausting, but there’s a high risk of getting a serious bite), we initially guessed that differences in the tendency to escalate fights may exist because males that can afford to lose more (“big and strong” males) were more willing to take the chance of having a costly encounter than scrawnier males. What we observed, however, was almost the exact opposite. Of the two males in each trial, we found that the wimpier of the two consistently responded to his competitor’s display behavior with more aggressive behaviors. The really cool part about this is that the tendency to respond with aggression isn’t hardwired— it’s not that small males were always more aggressive, but instead that the males that were smaller than their competitors were more aggressive. A nuanced, but important, distinction. Put a medium sized male with a bigger competitor, and he’d act like a tough guy; put the same lizard with a tiny competitor, and he wouldn’t bother to give the challenger the time of day. So, it seems like fence lizard males are somehow assessing their own chances of success in a fight against every individual competitor that they face, and adjusting their strategies accordingly. Being willing to escalate a fight may be crazy risky, but also could literally be the only way to defeat a physically formidable opponent. Littler guys need to be willing to take the risk in order to reproduce. Bigger males are more chill: there may be no need to waste time and energy doing displays when they don’t need to, since they’ve really got the size advantage if the confrontation were to come to blows (or bites!).